ProjectSummary Spinocerebellarataxias(SCAs)areneurodegenerativesyndromesofautosomalinheritance.Theyare characterizedbycerebellardysfunctionandmaybeassociatedwithotherneurologicalsignssuchasdystonia andmyoclonus.Nocureiscurrentlyavailableforthesesyndromes,largelybecausewelackadetailed understandingofthecellularmechanismscausingthedisease.TheMoonwalker(MWK)mouseisarodent modelofthehumanspinocerebellarataxia41(SCA41).ItcarriesagainoffunctionmutationoftheTRPC3 channel.CerebellarexpressionofTRPC3ishighlycell-specific,beingpresentonlyinPurkinjecells(PCs)and unipolarbrushcells(UBCs).IntheearlystagesoftheMWKataxiaPCsarefunctionallyimpairedandUBCs arealmostcompletelyablated.Thus,acriticalquestionraisedbytheMWKataxiamodeliswhethereitherthe PCimpairmentortheUBClosscanautonomouslycausethedisease,orwhetheracombinationofthetwois requiredtocausetheataxicphenotype.Toanswerthisquestionitisnecessarytoselectivelyexpressthe MWKmutationinoneandnottheothercelltype.Inordertodoso,weproposetomakeanewCre-dependent TRPC3mwkknock-inmouseline(TRPC3mwkfx)byusingageneticswitch(FLEx)strategy.Wewillbreedthese micewithPC-specificPcp2CremicetoselectivelydriveexpressionTRPC3mwkinPCsandwewillcharacterize themotorphenotypeandthecerebellarpathologyinthePC-specificTRPC3mwkmiceSuccessfulcompletionof theseexperimentswillshedlightonthepathogenicmechanismoftheMWKataxiaandwillallowdissectingthe selectivecontributionofPCimpairment.Thisnewtransgenic(TRPC3mwkfx)mousewillalsobeessentialfor futureexperimentsthatwilltakeadvantageofthismousetoselectivelyexpresstheMWKmutationinUBCs, andinvestigatetheroleoftheseneuronsintheMWKataxiaand,moreingeneral,inthecerebellarnetwork. Additionally,thismouselinemayalsohelpstudyingtheroleofTRPC3inothercellpopulationswherethis channelisexpressed,withinandoutsidetheCNS.